Glass fibers coated with thermoelectric lead telluride nanocrystals, shown in this scanning electron micrograph, could be wrapped around exhaust pipes to capture waste heat.

Credit: Nano Lett

Power Wrap

Glass fibers coated with thermoelectric lead telluride nanocrystals, shown in this scanning electron micrograph, could be wrapped around exhaust pipes to capture waste heat.

Credit: Nano Lett

By coating glass fibers with lead telluride nanocrystals, chemical engineers have made flexible thermoelectric devices that could one day capture waste heat and turn it into electricity (Nano Lett., DOI: 10.1021/nl300524j). Though preliminary, the work could lead to wrappings for pipes in power plants and car engines that improve energy efficiency.

Thermoelectric materials convert temperature differences into electricity. Today’s thermoelectric products are typically rigid and brittle. They consist of lead telluride or bismuth telluride crystals, or can be made by pressing powders of those materials into disks. To make devices, the crystal or disk is then carved into tiny pillars, an inefficient process that requires lots of the expensive material.

Purdue University’s Yue Wu and colleagues wanted to make flexible devices that could more easily conform to the irregular shapes of engines and exhaust pipes. So they coated inexpensive, bendable glass fibers with a thin layer of PbTe nanocrystals.

The researchers first suspended the nanocrystals in an organic solvent to make an ink. Then they repeatedly dipped the fibers into the ink to give them a 300-nm-thick nanocrystal coating. The researchers found that the fibers have a thermoelectric efficiency (ZT value) of more than 0.7 at 400 K, close to the 0.8 for PbTe crystals.

Compared with conventional thermoelectrics, Wu says, his materials exhibit “the same performance with much less material and lower cost. Our approach is straightforward and scalable.”

Before the researchers can test the fibers’ heat-harvesting capability in a car engine, they need to make their coatings more bendable: The current versions develop tiny cracks when bent significantly, though the cracks reseal when pressure on them releases.